>If you want to consider neanderthals as hibrids, what are the two species>that hybridize to produce them?

No, I don't consider neandertals hybrids. I think Europoids
are hybrids :-).. Just as we can find variations among dog
skeletons we can and should find variations among human
populations, but it doesn't mean that they are separate
species. Even today we have different size humans; that part
hasn't become uniform yet.